Currently there are many types of devices for measuring ionizing radiation including ion chambers, proportional counters, diode detectors, photographic film, and thermoluminescent devices.
Ion chambers measure the ionization in a known fixed volume of air by applying a voltage across that known volume and collecting any ion pairs that are created as ionizing radiation passes through the volume. Proportional counters work on a similar principle. Again, a known fixed volume of air or some other substance has a voltage applied across it. Unlike the ion chamber, this applied voltage is sufficiently high so that the ion pairs are substantially accelerated within the fixed volume. These accelerated ions collide with other molecules/atoms and create new ion pairs. The total number of ion pairs that will be collected now will be proportional to the number of ion pairs created by ionizing radiation as it passes through the volume.
Diode detectors are semiconductor diodes, normally made of a group IV semiconductor material. Typically the diode is back biased. Ionizing radiation passing through the depleted region of the diode will cause charge carriers to be generated there. These quickly drift though the depletion region and are collected through the bulk material making up the remainder of the diode.
Photographic film typically has a silver compound that is modified to form a latent image when it is exposed to ionizing or optical radiation. The film can then be developed. The amount of silver compound removed from the film will be a function of the amount of radiation that to which the film was exposed.
Thermoluminescent devices (TLD's) are normally made of a crystalline material. When a TLD is exposed to ionizing is radiation, there is resulting damage to the crystal structure and dislocation cites are created. These dislocations are metastable. When the TLD is heated, the crystal will change state and will radiate low energy photons. These photons are counted using some collection measurement equipment. Typically this would be a photomultiplier tube and the appropriate photon counting electronics. The number of photons counted will be a function of the collection equipment's dark current, its efficiency, and the number of dislocations created in the TLD by the ionizing radiation.
All of the detectors described above provide mechanisms for measuring ionizing radiation dose. Dose is simply the amount of energy deposited per unit mass. A problem is that the absorption cross section for any material is dependent on the radiation energy and the material's physical properties. Before any of the detectors described above are used to measure human exposure (often referred to as dose equivalent) the response of the human tissue over the expected energy range must be characterized. All subsequent measurements of dose must be converted to dose equivalent using a variety of calculation techniques that depend on such factors as the radiation type, ambient pressure and temperature. (See, e.g., Task Group 21 Report by the American Association of Physicists in Medicine or AAPM, and The Quality Factor in Radiation Protection from Report 40 of the
International Committee for Radiation Units and Measurement or ICRU) Methods are known for making tissue equivalent radiation detectors ( See, Microdosimetry and its Application to Biological Processes, Plenum Publishing Corp, 1986, Zaider, M. and Rossi, H. H.). These methods employ devices that are usually some sort of ion chamber or proportional counter filled with a gas having the same proportions of carbon, hydrogen, oxygen, and other elements as tissue.
There are many polymers or polymer composite materials that are radiation sensitive (e.g. U.S. Pat. No. 4,975,222 for "Radiation Detecting Elements and Method of Detection", Yoshino et. al.; U.S. Pat. No. 5,100,762 for "Radiation Sensitive Polymer and Radiation Sensitive Composition Containing The Same", Tanaka et. al.). Typically, these materials are used passively (i.e. not quantified in real time) to detect radiation. They may operate by forming fizzures that are subsequently measured or etched away photographically like film. They may be used in the processing and design of integrated circuits (e.g. U.S. Pat. No. 5,691,089 for "Integrated Circuits Formed in Radiation Sensitive Material and Method for Forming Same", Smayling et. al; U.S. Pat. No. 5,596,199 for "Passive Solid State Microdosimeter with Electronic Readout", McNulty et al.). These materials have also been used to produce active optical devices such as light emitting diodes and photodetectors (See U.S. Pat. No. 5,523,555 for "Photodetector Device Having a Semiconductive Conjugated Polymer", Friend et. al).